Continuous and uniform hologram recording method and uniformly recorded hologram

ABSTRACT

A hologram recording method wherein a transparent member for introducing a light beam into a recording material is designed so that the transparent member and the recording film can be uniformly brought into close contact with each other through an index matching liquid without damaging the recording film, and it is possible to stably carry out uniform and continuous exposure without failure of recording nor occurrence of unnecessary interference fringes. Also disclosed is a recorded hologram. A transparent member (3) is disposed at one surface of a recording film (2). A surface (5) of the transparent member (3) that is brought into close contact with the recording film (2) is convexly curved only in the direction of feed of the recording film (2). In addition, the space between the contact surface (5) and the recording film (2) is filled with an index matching liquid (4) so that the recording film (2) is brought into close contact with the transparent member (3) through the index matching liquid (4). In this state, a light beam is made incident on a surface (6) of the transparent member (3) other than the contact surface (5) so that the incident light beam reaching the recording film (2) through the contact surface (5) and the light beam reflected from the interfacial boundary between the reverse surface of the recording film (2) and the air interfere with each other in the recording film (2), thereby forming and recording interference fringes in the recording film (2).

BACKGROUND OF THE INVENTION

The present invention relates to a hologram recording method and arecorded hologram. More particularly, the present invention relates to amethod of continuously recording holographic interference fringes in arecording film, and also relates to a recorded hologram.

As a method of recording holographic interference fringes, it iswell-known practice to make light incident normally on a recordingmaterial. There are, however, cases where a beam of light is madeincident on the surface of a recording material at a relatively smallangle thereto in order to select various pitches for interferencefringes to be recorded. However, as the angle of incidence with respectto the surface of the recording material decreases, the rate at whichthe incident light is reflected due to the refractive index differencebetween the air and the recording material rises, resulting in areduction in the quantity of light entering the recording material.Consequently, the energy of light entering the inside of the hologramdry plate per unit of time decreases, and the exposure time lengthenscorrespondingly. To cope with the problem experienced when light is madeincident on the surface of the recording material at a relatively smallangle, the conventional practice has been to allow the light beam toenter the recording material through a transparent member having anincidence surface approximately perpendicular to the incident light. Forthis purpose, a glass block or a prism is used as a transparent member.

FIG. 17 shows an example in which glass blocks are used. A pair of glassblocks 42 and 43 each having a refractive index close to that of arecording material 41 are brought into close contact with both sides,respectively, of the recording material 41, and light beams 44 and 45are made incident on the surfaces of the recording material 41 throughthe glass blocks 42 and 43, thereby eliminating reflection at thesurfaces of the recording material 41 and increasing the amount ofenergy incident per unit of time, and thus enabling the desired hologramto be recorded efficiently.

FIG. 18 shows an example in which prisms are used as transparentmembers. A pair of prisms 46 and 47 are disposed on both sides,respectively, of the recording material 41 in the same way as in thearrangement shown in FIG. 17 so that light beams 44 and 45 which areincident substantially normally on the respective surfaces of the prisms46 and 47 interfere with each other in the recording material 41,thereby recording the desired hologram.

There has also been proposed a technique whereby a glass block isrotated so that the incidence surface of the glass block is alwaysperpendicular to the incident light beam, although not shown in theaccompanying drawings, (see Japanese Patent Application Laid-Open(KOKAI) No. 3-237481).

In addition, Japanese Patent Application Laid-Open (KOKAI) Nos. 1-154079and 3-271788 disclose a method wherein a plane of a transparent memberis brought into close contact with a recording film to expose the filmthrough the transparent member, thereby continuously producing aholographic mirror.

However, the conventional hologram recording method in which transparentmembers are brought into close contact with both sides of a recordingmaterial suffers from the problem that exceedingly large transparentmembers are needed particularly when exposure is effected over a largearea, so that the system becomes costly and bulky and also increases inweight.

The conventional method in which a holographic mirror is continuouslyproduced by effecting exposure through a transparent member is a methodfor forming interference fringes parallel to the surface of a recordingfilm and not a method for continuously forming interference fringesinclined with respect to the film surface. To reflect sunbeams incidentalong a direction other than the normal direction as in the case of aheat ray reflecting film in particular, it is preferable to recordinterference fringes inclined with respect to the film surface becausethe reflection efficiency can be considerably increased by doing so, asdescribed later.

With the conventional method, a holographic mirror can be recorded inprinciple, but since the interface of close contact between therecording film and the transparent member used for the incidence of alight beam is a plane, many problems as stated below occur in practice,causing the quality of the produced hologram to be degraded:

Firstly, the recording film may be damaged when contacted by the edge ofthe transparent member.

Secondly, since the interface between the recording film and thetransparent member is a plane, air bubbles inevitably get mixed in theindex matching liquid, causing a failure of holographic recording inregions where the air bubbles are present.

Thirdly, since the amount of index matching liquid to be supplied islarge due to the structure of the recording system, the index matchingliquid is likely to become non-uniform. In addition, the transparentmember and the recording film are contaminated with the index matchingliquid. Therefore, it is likely that unnecessary interference fringeswill occur and the diffraction characteristics will become non-uniform.

Fourthly, since the recorded interference fringes lie in only onedirection (parallel to the film surface) and cannot be multiplexed, itis difficult to obtain a holographic mirror providing a wide diffractionspectrum as in the case of a heat ray reflecting film.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above-describedproblems, and it is an object of the present invention to provide ahologram recording method wherein a transparent member for introducing alight beam into a recording material is designed so that the transparentmember and the recording film can be uniformly brought into closecontact with each other through an index matching liquid withoutdamaging the recording film, and it is possible to stably carry outuniform and continuous exposure without failure of recording noroccurrence of unnecessary interference fringes and to mass-produceuniform, non-defective holograms having a large area, and also provide arecorded hologram.

To attain the above-described object, the present invention provides ahologram recording method which is based on the principle that atransparent member having a surface convexly curved only in thedirection of feed of a continuously fed recording film is brought intoclose contact with one surface of the recording film by the combinationof its own weight and tension applied to the recording film, or therecording film is brought into close contact with the transparentmember, which is fixed, by tension applied to the recording film, and alight beam is made incident on one surface of the transparent member sothat the incident light beam reaching the recording film and the lightbeam reflected from the interfacial boundary between the reverse surfaceof the recording film and the air interfere with each other in therecording film, thereby forming and recording interference fringes inthe recording film.

That is, the hologram recording method of the present invention is amethod of recording a hologram in a continuously fed recording film bythe interference of light. A transparent member is disposed at onesurface of the recording film. A surface of the transparent member thatis brought into close contact with the recording film is convexly curvedonly in the direction of feed of the recording film. In addition, thespace between the contact surface of the transparent member and therecording film is filled with an index matching liquid so that therecording film is brought into close contact with the transparent memberthrough the index matching liquid. In this state, a light beam is madeincident on a surface of the transparent member other than the contactsurface thereof so that the incident light beam reaching the recordingfilm through the contact surface and the light beam reflected from theinterfacial boundary between the reverse surface of the recording filmand the air interfere with each other in the recording film, therebyforming and recording interference fringes in the recording film.

In this case, the light beam, which is made incident on a surface of thetransparent member other than the contact surface thereof, may be alight beam that is reciprocated to scan in a direction intersecting thedirection of feed of the recording film so that the scanning light beamreaching the recording film through the contact surface and the lightbeam reflected from the interfacial boundary between the reverse surfaceof the recording film and the air interfere with each other in therecording film, thereby forming and recording interference fringes inthe recording film. Further, a surface of the recording film on a sidethereof which will not come in contact with the transparent member maybe formed with a layer having a thickness distribution in a directionperpendicular to the direction of feed of the recording film so that theincident light beam is reflected at the surface of this layer.

Preferably, surfaces of the transparent member, exclusive of the lightbeam incidence surface and the contact surface, have previously beensubjected to a light-absorbing treatment, and portions of the recordingfilm other than the irradiated portion thereof are shielded from light.

Furthermore, the transparent member is preferably made of a materialhaving a refractive index differing from that of the recording film by0.2 or less in the temperature range of from 15° C. to 25° C. Specificexamples of such a material are as follows: When the principal componentof the recording film is a polyvinyl carbazole derivative, thetransparent member is preferably made of F2 glass, a polyester resin, anallyl resin having a high refractive index, or an acrylic resin having ahigh refractive index; when the principal component of the recordingfilm is a polyvinyl acetate derivative, the transparent member ispreferably made of BK-7 glass or quartz glass; and when the principalcomponent of the recording film is a polyester, the transparent memberis preferably made of F2 glass.

The light beam is preferably made incident on the light incidencesurface of the transparent member at an angle of 90°±10° to it.

The curvature radius of the contact surface of the transparent member ispreferably in the range of from 10 mm to 100 mm. Furthermore, the anglemade between one side surface of the transparent member and therecording film when the recording film comes in contact with the contactsurface of the transparent member and the angle made between anotherside surface of the transparent member and the recording film when therecording film comes out of the contact with the contact surface areboth preferably in the range of from 5° to 45°.

In addition, the size of the incident light beam in the direction offeed of the recording film is preferably not larger than 3 mm withregard to beam sizes which provide at least 13.5% of the maximumintensity.

It is also preferable that a tension of 10 kg/m to 50 kg/m should beapplied to the recording film, and that the thickness of the indexmatching liquid between the recording film and the contact surfaceshould be not larger than 500 μm.

It should be noted that the transparent member may be disposed at eitherthe upper or lower side of the recording film.

Incidentally, when the surface of the recording film that will not comein contact with the transparent member is formed with a layer having athickness distribution in a direction perpendicular to the direction offeed of the recording film, the layer may have a thickness distributionin which the layer thickness gradually increases. In such a case, theangle between the surface of the layer having the thickness distributionand the surface of the recording film may be larger than 0° and notlarger than 10°. In this case, interference fringes recorded in therecording film can be inclined at an angle larger than 0° and not largerthan 10° to the film surface.

Another hologram recording method of the present invention is a methodof recording a hologram in a continuously fed recording film by theinterference of light. The recording film is sandwiched between atransparent member disposed at a side where a light beam enters and areflector disposed at a side where the light beam reflects. Thetransparent member has a light incidence surface at a portion thereofother than the surface thereof which is in contact with the recordingfilm, and the light beam is made incident on the light incidence surfaceof the transparent member so that the incident light beam reaching therecording film and the light beam transmitted by the recording film andreflected from a reflecting surface of the reflector interfere with eachother in the recording film, thereby forming and recording interferencefringes in the recording film.

In this case, the reflecting surface and the surface of the recordingfilm may be disposed at an angle to each other to vary the angle of thereflected light beam to thereby record oblique interference fringes inthe recording film.

It is also possible to form the reflecting surface in a staircase shapeso as to make an angle between the reflecting surface and the surface ofthe recording film, thereby varying the angle of the reflected lightbeam, and thus recording oblique interference fringes in the recordingfilm.

The reflecting surface may have a holographic reflecting layer thereonso that the angle of the reflected light beam is varied by theholographic reflecting layer, thereby recording oblique interferencefringes in the recording film.

Furthermore, it is preferable to use a linear light beam as the incidentlight beam and to feed the recording film along the respective recordingfilm contact surfaces of the transparent member and the reflector. Therecording film contact surfaces of the transparent member and thereflector are preferably arranged such that one of the two contactsurfaces is a convex surface and the other is a concave surface. Inaddition, the space between the recording film and the transparentmember and/or the space between the recording film and the reflector ispreferably filled with an index matching liquid so that the recordingfilm is brought into close contact with the transparent member and/orthe reflector through the index matching liquid. It should be noted thatthe difference between the refractive indices of the transparent member,the recording film and the index matching liquid is preferably notlarger than 0.2 in the temperature range of from 15° C. to 25° C.

It is also possible to form the reflector of a transparent material sothat the difference between the refractive indices of the reflector, therecording film and the index matching liquid is not larger than 0.2 inthe temperature range of from 15° C. to 25° C.

The reflecting surface of the reflector may be the above-describedrecording film contact surface or a surface other than it. Thereflecting surface may define an interface in cooperation with the air.It is also possible to form a mirror reflecting layer on the reflectingsurface.

Furthermore, surfaces of the two transparent members, exclusive of thelight incidence surface and the recording film contact surfaces, arepreferably light-absorbing surfaces, and portions of the recording filmother than the portion thereof where the interference is to be causedare preferably shielded from light.

It should be noted that the angle between the normal to the lightincidence surface and the incident light beam is preferably in the rangeof from 0° to 10°.

Still another hologram recording method of the present invention is amethod of recording a hologram in a continuously fed recording film bythe interference of light. The recording film is wound on amirror-finished, light-reflecting roll, and a transparent member isbrought into close contact with the upper side of the recording film.While the recording film is continuously fed by rotating the roll, alight beam is made incident substantially normally on one surface of thetransparent member so that the incident light beam and the light beamreflected from the mirror surface of the roll interfere with each otherin the recording film, thereby forming and recording interferencefringes in the recording film.

In this case, the arrangement may be such that the transparent member isdisposed at the lower side of the roll and the surface of thetransparent member that faces the roll has the same arcuateconfiguration as that of the surface of the roll and that the spacebetween the arcuate portion of the transparent member and the roll isfilled with an index matching liquid so that the roll is brought intoclose contact with the transparent member through the index matchingliquid by making use of gravity. Preferably, surfaces of the transparentmember on which no light beam will be incident have previously beensubjected to a light-absorbing treatment.

The hologram of the present invention is a hologram comprising equallyspaced interference fringes recorded in a recording film in parallel toat least one direction of the plane of the recording film. Theinterference fringes are recorded such that the disorder of theinterference fringes in a cross-section along the above direction islarger than the disorder of the interference fringes in a cross-sectionalong a direction perpendicular to the first-mentioned direction.

In this case, the interference fringes may be recorded such that thosein the cross-section along the direction perpendicular to thefirst-mentioned direction are at an angle to the plane of the recordingfilm.

Thus, according to the present invention, a transparent member isdisposed at one surface of a recording film, and the space between therecording film and the film contact surface of the transparent member isfilled with an index matching liquid so that the recording film isbrought into close contact with the transparent member through the indexmatching liquid. In this state, a light beam is made incident on asurface of the transparent member other than the recording film contactsurface so that the incident light beam reaching the recording filmthrough the contact surface and the light beam reflected from theinterfacial boundary between the reverse surface of the recording filmand the air interfere with each other in the recording film, therebyforming and recording interference fringes in the recording film.Accordingly, even if the angle of incidence of the light beam to thesurface of the recording film is small, exposure of high efficiency canbe realized. In addition, it is possible to select various pitches forinterference fringes to be recorded by varying the angle of the incidentlight beam to the surface of the recording film.

If a recording film of continuous length is subjected to exposure usinga linear light beam while being continuously fed, it becomes possible toreadily produce a uniform, high-quality hologram having a large area.Thus, it is possible to provide a hologram producing method which givesa high yield and is suitable for mass-production.

Further, a surface of the transparent member that is brought into closecontact with the recording film is convexly curved only in the directionof feed of the recording film, and the space between the recording filmcontact surface and the recording film is filled with an index matchingliquid so that the recording film is brought into close contact with thetransparent member through the index matching liquid. Therefore, thecondition of contact between the recording film and the transparentmember improves, so that the recording film moves smoothly when fed.Accordingly, the recording film will not be flawed by contact with thecontact surface of the transparent member, and no air bubbles will getmixed in the index matching liquid. Thus, the thickness of the indexmatching liquid can be made small and uniform. In addition, the reversesurface of the recording film will not be contaminated with the indexmatching liquid, and the recording film can be uniformly irradiated withthe incident light beam and the reflected light beam. Accordingly, it ispossible to continuously record a uniform, excellent hologram having alarge area. Furthermore, interference fringes can be formed in therecording film such that a large number of interference fringes slightlydifferent in the angle of inclination are superimposed one on top ofanother by virtue of the configuration of the contact surface of thetransparent member. Therefore, a holographic mirror thus recorded in therecording film provides a diffraction spectrum which is not a linespectrum but a broad band spectrum. Accordingly, it is possible toobtain a holographic mirror suitable for a solar reflector of the likewhich reflects light only in the infrared region.

If a surface of the recording film that will not come in contact withthe transparent member is formed with a layer having a thicknessdistribution in a direction perpendicular to the direction of feed ofthe recording film so that the incident light beam is reflected at thislayer, it is possible to form interference fringes inclined with respectto the surface of the recording film. Thus, the method is suitable forproduction of a solar reflector or the like.

If surfaces of the transparent member, exclusive of the light beamincidence surface and the recording film contact surface, havepreviously been subjected to a light-absorbing treatment, it is possibleto prevent irregular reflection and to minimize the disorder ofinterference fringes. In addition, no light will impinge on portions ofthe recording film other than the exposed portion thereof. Thus, itbecomes unnecessary to install a large-sized light-shielding plate.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction,combinations of elements, and arrangement of parts which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one form of arrangement for carrying out the hologramrecording method of the present invention.

FIG. 2 shows a cross-section of a transparent member which isperpendicular to the direction of movement of a recording film.

FIG. 3 shows one example of an optical system for forming a linear lightbeam.

FIG. 4 shows another form of arrangement for carrying out the hologramrecording method of the present invention.

FIG. 5 shows one example of an optical system for forming a scanninglight beam.

FIG. 6 is a sectional view similar to FIG. 2, showing a form forrecording inclined interference fringes.

FIG. 7 shows still another form of arrangement for carrying out thehologram recording method of the present invention.

FIG. 8 shows a cross-section of a transparent member in the arrangementshown in FIG. 7, which is perpendicular to the direction of movement ofa recording film.

FIG. 9 shows a modification of a reflector in the arrangement shown inFIG. 8.

FIG. 10 is a view for explanation of another recording method of thepresent invention.

FIG. 11 is a view for explanation of the method shown in FIG. 10 in acase where it is applied to a continuous exposure, roll-feed system.

FIG. 12 is a view for explanation of an antireflection treatment.

FIG. 13 is a view for explanation of a recording method in which atransparent member is disposed at the lower side of a roll.

FIG. 14 is a view for explanation of one embodiment of the recordingmethod shown in FIG. 10.

FIG. 15 is a graph showing an example of measurement of the diffractionefficiency obtained from a volume hologram.

FIG. 16(a) schematically shows a configuration of holographicinterference fringes which have a cross-section perpendicular to thedirection of movement of the recording film and which are recorded bythe device shown in FIGS. 1 and 2.

FIG. 16(b) schematically shows a configuration of holographicinterference fringes which have a cross-section parallel to thedirection of movement of the recording film and which are recorded bythe device shown in FIGS. 1 and 2.

FIG. 16(c) schematically shows a configuration of holographicinterference fringes which have a cross-section perpendicular to thedirection of movement of the recording film and which are recorded bythe device shown in FIGS. 1 and 6.

FIG. 16(d) schematically shows a configuration of holographicinterference fringes which have a cross-section parallel to thedirection of movement of the recording film and which are recorded bythe device shown in FIGS. 1 and 6.

FIG. 17 is a view for explanation of a conventional hologram recordingmethod.

FIG. 18 is a view for explanation of another conventional hologramrecording method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The hologram recording method of the present invention will be describedbelow more specifically by way of preferred embodiments.

FIG. 1 shows one example of a system arrangement for carrying out thehologram recording method of the present invention. In FIG. 1, referencenumeral 1 denotes a series of rolls, 2 a recording film, and 3 atransparent member. The series of rolls 1 feeds the recording film 2 tothe transparent member 3. A feed nozzle 8 supplies the recording film 2with an index matching liquid 4 upstream the transparent member 3. Thetransparent member 3 has a contact surface 5 with which the recordingfilm 2 is brought into close contact through the index matching liquid4.

FIG. 2 is a sectional view taken along the line A--A' in FIG. 1. InFIGS. 1 and 2, the same reference numerals denote the same elements orportions. Referring to these figures, the transparent member 3 has alight beam incidence surface 6 provided on one side thereof at apredetermined angle to the contact surface 5. Reference numeral 11denotes a linear incident light beam. Reference numeral 7 denotes theother surface of the recording film 2 that is not in contact with thetransparent member 3, and 12 a reflected light beam.

Although not shown, surfaces of the transparent member 3, exclusive ofthe light beam incidence surface 6 and the recording film contactsurface 5, are light-absorbing surfaces, and portions of the recordingfilm 2 other than a portion thereof where interference is to be causedare shielded from light.

In the above-described arrangement, the light beam 11 is made incidentsubstantially normally on the incidence surface 6. If the angle betweenthe incident light beam 11 and the normal to the incidence surface 6 islarge, reflection occurs at the incidence surface 6, causing the lightbeam utilization efficiency to be lowered. Therefore, the angle of theincident light beam 11 to the normal to the incidence surface 6 ispreferably in the range of from 0° to 10°. The incident light beam 11rectilinearly propagates through the transparent member 3 and reachesthe contact surface 5. The refractive indices of the recording film 2,the transparent member 3 and the index matching liquid 4 areapproximately equal to each other. Consequently, the incident light beam11 enters the recording film 2 without reflecting at the interfacebetween the contact surface 5 and the index matching liquid 4 or at theinterface between the index matching liquid 4 and the recording film 2and impinges on the other surface 7 of the recording film 2. If theangle 8 between the incident light beam 11 and the contact surface 5 ofthe transparent member 3 is small, the incident light beam 11 totallyreflects at the interface between the surface 7 of the recording film 2,which is not in contact with the transparent member 3, and the air(n≈1.0), so that the incident light beam 11 and the reflected light beam12 interfere with each other in the recording film 2. Thus, interferencefringes are formed and recorded in the recording film 2.

In the example shown in FIG. 1, the contact surface 5 of the transparentmember 3 has a convex cylindrical configuration. Accordingly, therecording film 2 can be brought into close contact with the transparentmember 3 under favorable conditions with the index matching liquid 4interposed therebetween, so that the recording film 2 can move smoothlywhen fed without being flawed by contact with the contact surface 5 ofthe transparent member 3 and no air bubbles will get mixed in the indexmatching liquid 4. Thus, the thickness of the index matching liquid 4can be made small and uniform. In addition, the reverse surface 7 of therecording film 2 will not be contaminated with the index matching liquid4, and the recording film 2 can be uniformly irradiated with theincident light beam 11 and the reflected light beam 12. Accordingly, itis possible to continuously record a uniform, excellent hologram havinga large area. For this purpose, it is generally preferable that thecurvature radius of the cylindrical contact surface 5 should be in therange of from 10 mm to 100 mm, and that the tension applied to therecording film 2 should be in the range of from 10 kg/m to 50 kg/m, andfurther that the thickness of the index matching liquid 4 should be notlarger than 500 μm. Furthermore, the angle α (see FIG. 1) made betweenone side surface of the transparent member 3 and the recording film 2when the recording film 2 comes in contact with the contact surface 5and the angle β (see FIG. 1) made between another side surface of thetransparent member 3 and the recording film 2 when the recording film 2comes out of the contact with the contact surface 5 are both preferablyin the range of from 5° to 45°. In addition, the size of the incidentlight beam 11, which has a linear cross-sectional configuration, in thedirection of feed of the recording film 2 is preferably not larger than3 mm with regard to beam sizes which provide at least 1/e² =13.5% of themaximum intensity.

As has been described above, the transparent member 3 is preferably madeof a material having a refractive index close to that of the recordingfilm 2. Since the refractive index of the recording film 2 is generallyin the range of from 1.3 to 1.7, it is possible to use glass, a plasticmaterial, or an inorganic substance as a material for the transparentmember 3, as described later. It should be noted that since therecording film 2 is exposed to a linear light beam appliedperpendicularly to the direction of feed of the recording film 2, theexposure is not substantially affected by vibration; however, if thebeam irradiation time is long, glass, which has sufficiently large massand is not readily vibrated, is preferably used as a material for thetransparent member 3.

Thus, in the present invention, the recording film 2 is subjected tolinear exposure while being continuously fed in close contact with theconvex cylindrical contact surface 5 of the transparent member 3.Accordingly, it is only necessary for the transparent member 3 to have asize required for the linear exposure, which is smaller than that in thecase of planar exposure. Thus, the transparent member 3 is small in sizeand light in weight and also less costly. In addition, since exposurecan be effected with the recording film 2 brought into close contactwith the transparent member 3 under favorable conditions, it is possibleto realize a hologram of large area and uniform quality. Since a linearlight beam is used, there is substantially no effect of vibration on theexposure. Furthermore, since the surface 7 of the recording film 2 thattotally reflects the incident light beam 11 becomes a convex cylindricalsurface along the contact surface 5 of the transparent member 3, thereflected light beam 12 is not a parallel light beam but a slightlyconverging light beam. Accordingly, interference fringes formed byinterference between the incident light beam 11 and the reflected lightbeam 12 have a configuration wherein a large number of interferencefringes slightly different in the angle of inclination are superimposedone on top of another. FIG. 16(a)and 16(b) shows schematicallyconfigurations of interference fringes in cross-sections perpendicularand parallel, respectively, to the direction of movement of therecording film 2 in a hologram recorded by the arrangement shown inFIGS. 1 and 2. As will be clear from the figure, the hologram recordedby the above-described method of the present invention contains equallyspaced interference fringes recorded in the recording film 2 in parallelto either direction of the plane of the film 2. However, the disorder ofthe interference fringes in the cross-section parallel to the directionof movement of the recording film 2 is larger than that of theinterference fringes in the cross-section perpendicular to the directionof movement of the recording film 2. This is the effect produced by theabove-described recording along the convex cylindrical surface. Aholographic mirror produced in this way provides a diffraction spectrumwhich is not a line spectrum but a broad band spectrum due to thedisorder of the interference fringes and is therefore suitable for asolar reflector or the like which reflects light only in the infraredregion.

It should be noted that in FIG. 1 reference numeral 9 denotes a linearexposure region, and 10 an incidence region of the incidence surface 6on which the incident light beam 11 is incident. The incident light beam11 may be formed, for example, by an arrangement as shown in FIG. 3.That is, a narrow laser beam 13 is passed through a plano-concavecylindrical lens 14 and a plano-convex cylindrical lens 15, which aredisposed in confocal relation to each other, so that the laser beam 13is enlarged in one direction.

As shown in FIG. 2, the incident light beam 11 enters the incidencesurface 6 of the transparent member 3 at substantially right anglesthereto through the incidence region 10 and is reflected at the othersurface 7 of the recording film 2. If reflection occurs elsewhere thanthe surface 7, the reflected light undesirably enters the recording film2 and disorders the interference fringes. Therefore, surfaces oftransparent member 3, exclusive of the incidence surface 6 and thecontact surface 5, have previously been subjected to a light-absorbingtreatment, thereby preventing irregular reflection. Thus, it is possibleto prevent light from undesirably entering an unexposed or exposedportion of the recording film 2 and to thereby prevent the interferencefringes from being disordered without the need for installing alarge-sized light-shielding plate.

The difference in refractive index between the recording film 2, thetransparent member 3 and the index matching liquid 4 is preferably notlarger than 0.2, more preferably not larger than 0.1, in the temperaturerange of from 15° C. to 25° C. Specific examples of the material of thetransparent member 3 are as follows: When the principal component of therecording film 2 is a polyvinyl carbazole derivative, the transparentmember 3 is preferably made of F2 glass, a polyester resin, an allylresin having a high refractive index, an acrylic resin having a highrefractive index, etc. When the principal component of the recordingfilm 2 is a polyvinyl acetate derivative, the transparent member 3 ispreferably made of BK-7 glass, quartz glass, etc. When the principalcomponent of the recording film 2 is a polyester, the transparent member3 is preferably made of F2 glass or the like.

The arrangement of the present invention may also be such that atransparent member 3 which is similar to the above is disposed at thelower side of the recording film 2, as shown in FIG. 4. In thearrangement shown in FIG. 4, the recording film 2 winds on the convexcylindrical contact surface 5 of the transparent member 3 through theindex matching liquid 4 in the same way as in the case of thearrangement shown in FIG. 1. Therefore, if tension is applied to therecording film 2 by two pairs of rolls 1 respectively disposed upstreamand downstream the transparent member 3 so that the recording film 2presses the transparent member 3 from above it, the condition of contactbetween the transparent member 3 and the recording film 2 is improved,and unnecessary stray light can be eliminated. Thus, a hologram of goodquality can be produced. In this case also, it is preferable thatsurfaces of the transparent member 3, exclusive of the light beamincidence surface 6 and the contact surface 5, have previously beensubjected to a light-absorbing treatment.

In the foregoing arrangements, the linear incident light beam 11 formedby an optical system as shown in FIG. 3 is made incident on theincidence surface 6 of the transparent member 3 to irradiate the linearexposure region 9 simultaneously at all times. However, it is alsopossible to irradiate the linear exposure region 9 with a scanning lightbeam reciprocating at high speed. FIG. 5 shows one example of an opticalsystem which may be used for this purpose in place of the optical systemshown in FIG. 3. In this optical system, laser light oscillated from alaser light source 50 is deflected by a galvanomirror 51 and convertedinto a parallel-moving scanning beam by a parabolic mirror 52. Then, thebeam is reflected by mirrors 53 and 54 so as to enter the linearincidence region 10 on the incidence surface 6 of the transparent member3 as a scanning light beam 11' reciprocating as shown by the double-headarrow in the figure. Accordingly, the scanning light beam 11' is appliedsubstantially perpendicularly to the direction of movement of therecording film 2, and the incident light beam 11' is totally reflectedat the other surface 7 of the recording film 2 so that the incidentlight beam 11' and the reflected light beam interfere with each other inthe recording film 2, thereby sequentially recording interferencefringes in the transverse direction of the recording film 2.

The merit of using the reciprocating scanning light beam 11' is asfollows. When a light beam 11 linearly enlarged by using an opticalsystem as shown in FIG. 3 is employed, the light intensity at an endportion is weaker than that in the central portion, resulting innon-uniformity of light intensity in the recording plane, whereas, whena scanning light beam 11' as shown in FIG. 5 is employed, suchnon-uniformity of light intensity in the recording plane does not occur.It is necessary in order to realize such uniform exposure to allow therecording film 2 to move only a distance shorter than a half of thewidth of the beam 11' during one reciprocation of the beam 11'. That is,it is necessary to satisfy the following relationship:

    2d/s≦c/2a

where c is the width of the beam 11',

s is the scanning speed,

d is the width of the recording film 2, and

a is the feed speed.

Incidentally, a holographic mirror produced by the above method hasinterference fringes parallel to the surface of the recording film.However, when such a holographic mirror is pasted on a window glass, forexample, to use it as a solar reflector for reflecting infrared rays, itis preferable for the interference fringes to be inclined at a desiredangle to the surface of the recording film. FIG. 15 shows a specificexample of measurement of the diffraction efficiency obtained from avolume hologram comprising parallel interference fringes. When light isincident obliquely (64°) on the interference fringes, the diffractionefficiency becomes lower than in the case of the normal incidence (90°)on the interference fringes, and the diffraction wavelength undesirablyshifts toward the short wavelength side. It can be said that thisphenomenon generally occurs from the theory of diffraction. Accordingly,in the case of a window on which sunlight is obliquely incident fromabove it, it is preferable, with a view to reflecting and diffractingthe desired wavelength as designed and at high diffraction efficiency,to enable interference fringes to be recorded at an angle to the surfaceof the recording film so that the interference fringes are perpendicularto the incident light.

FIG. 6 is a sectional view similar to FIG. 2, showing one example ofrecording interference fringes inclined with respect to the surface ofthe recording film 2 as described above. The inclined interferencefringes are recorded by using the system arrangement shown in FIG. 1.This example differs from the example shown in FIG. 2 only in thearrangement of the recording film 2. The second example will beexplained below with reference to FIGS. 1 and 6. FIG. 6 is a sectionalview taken along the line A--A' in FIG. 1. In these figures, the samereference numerals denote the same elements or portions. In FIGS. 1 and6, the transparent member 3 is arranged as described above. The side ofthe recording film 2 that is reverse to the side that comes in closecontact with the transparent member 3 is provided with a protective film16 having a wedge-shaped cross-sectional configuration as shown in FIG.6.

In the above-described arrangement, the refractive indices of therecording film 2, the protective film 16, the transparent member 3 andthe index matching liquid 4 are made substantially equal to each other.Consequently, the incident light beam 11 enters the protective film 16without reflecting at the interface between the contact surface 5 andthe index matching liquid 4 or at the interface between the indexmatching liquid 4 and the recording film 2 or at the interface betweenthe recording film 2 and the protective film 16 and impinges on thereverse slanted surface 17 of the protective film 16. Since the angle Θ₂between the incident light beam 11 and the reverse surface 17 of theprotective film 16 is small, the incident light beam 11 is totallyreflected at the interface between the surface 17 and the air (n≈1.0),so that the incident light beam 11 and the reflected light beam 12interfere with each other in the recording film 2. Thus, interferencefringes inclined with respect to the surface of the recording film 2 areproduced and recorded in the film 2. In this hologram producing method,the angle Θ₃ between the reverse surface 17 of the protective film 16and the recording film 2 can be set in the range of from 0° to 10°.Accordingly, the angle of inclination of the interference fringes of asolar reflector thus produced is in the range of from 0° to 10° withrespect to the surface of the recording film 2. It should be noted thatif the angle Θ₂ is large, aluminum or the like may be deposited on theexposed surface 17 of the protective film 16 to form a mirror reflectinglayer or a holographic reflecting layer.

In this case also, the contact surface 5 of the transparent member 3 hasa convex cylindrical configuration in the same way as in the arrangementshown in FIG. 2. Accordingly, the recording film 2 can be brought intoclose contact with the transparent member 3 under favorable conditionswith the index matching liquid 4 interposed therebetween, so that therecording film 2 can move smoothly when fed without being flawed bycontact with the contact surface 5 of the transparent member 3 and noair bubbles will get mixed in the index matching liquid 4. Thus, thethickness of the index matching liquid 4 can be made small and uniform.In addition, the reverse surface 7 of the recording film 2 will not becontaminated with the index matching liquid 4, and the recording film 2can be uniformly irradiated with the incident light beam 11 and thereflected light beam 12. Accordingly, it is possible to continuouslyrecord a uniform, excellent hologram having a large area. Furthermore,it is only necessary for the transparent member 3 to have a sizerequired for the linear exposure, which is smaller than that in the caseof planar exposure. Thus, the transparent member 3 is small in size andlight in weight and also less costly. In addition, since a linear lightbeam is used, there is substantially no effect of vibration on theexposure. Furthermore, since the reverse surface 17 of the protectivefilm 16 that totally reflects the incident light beam 11 becomes aconvex cylindrical surface along the contact surface 5 of thetransparent member 3, the reflected light beam 12 is not a parallellight beam but a slightly converging light beam. Accordingly,interference fringes formed by interference between the incident lightbeam 11 and the reflected light beam 12 have a configuration wherein alarge number of interference fringes slightly different in the angle ofinclination are superimposed one on top of another. FIG. 16(b) showsschematically configurations of interference fringes in cross-sectionsperpendicular and parallel, respectively, to the direction of movementof the recording film 2 in a hologram recorded by the arrangement shownin FIGS. 1 and 6. As will be clear from the figure, the hologramrecorded by the above-described method of the present invention containsequally spaced interference fringes recorded in the recording film 2 inparallel to the film plane in the direction of movement of the recordingfilm 2 but at an angle to the plane of the recording film 2 in thedirection perpendicular to the direction of movement of the recordingfilm 2. Further, the disorder of the interference fringes in thecross-section parallel to the direction of movement is larger than thatof the interference fringes in the cross-section perpendicular to thedirection of movement of the recording film 2. This is the effectproduced by the above-described recording along the convex cylindricalsurface. A holographic mirror produced in this way provides adiffraction spectrum which is not a line spectrum but a broad bandspectrum due to the disorder of the interference fringes and istherefore suitable for a solar reflector or the like which reflectslight only in the infrared region.

Incidentally, the protective film 16 having a wedge-shapedcross-sectional configuration may be formed on one surface of therecording film 2 by any of various methods, for example, a methodwherein a liquid is coated and dried on the surface of the recordingfilm 2 such that the desired film thickness distribution is attained,and a method wherein a film having the desired thickness distribution ispasted on the surface of the recording film 2. There are various typesof method of coating the surface of the recording film 2 with a liquidwith the desired film thickness distribution, for example, a die coatingmethod wherein the slit width is varied in conformity to the desiredfilm thickness distribution pattern, a die coating method wherein thefeed rate is varied in conformity to the desired film thicknessdistribution pattern by controlling the applied pressure, a methodwherein after being subjected to dip coating, the base material ishorizontally transported in an erected position with one side edgethereof facing downward so that the thickness of the applied coatingliquid gradually increases toward the lower edge, and a method wherein acoating liquid is poured on the base material placed in an erectedposition and the base material is horizontally transported so that thethickness of the applied coating liquid gradually increases toward thelower edge of the base material. Any of these methods may be employed,provided that optimal conditions are set to obtain an appropriate filmthickness distribution. Important factors are the viscosity of thecoating liquid and the drying rate. In the case of die coating, theviscosity of the coating liquid is preferably not lower than 100 cps,and drying is preferably effected by heat immediately after the coatingliquid has passed through the slit. If heated air is strongly applied tothe coating, the film surface is disordered. Therefore, an infraredheater is preferably used jointly with heated air with a view toenhancing the drying effect.

It should be noted that if the angle of incidence of the light beam 11on the surface 17 of the protective film 16 is 60° or more with respectto the normal, the incident light beam 11 totally reflects at theinterface between the protective film 16 and the air as long as therefractive index of the protective film 16 is 1.15, and it is thereforepossible to record interference fringes satisfactorily. However, it isnecessary in order to prevent total reflection at the interface betweenthe recording film 2 and the protective film 16 that the relationshipbetween the refractive index n₁ of the recording film 2 and therefractive index n₂ of the protective film 16 satisfy the condition ofn₂ /n₁ ≧0.866 from Snell's law. More specifically, it is possible to useas a material for the protective film 16 an aqueous solution ofpolyvinyl alcohol (the refractive index can be adjusted in the range offrom 1.494 to 1.557 by controlling the degree of saponification), apoly(p-hydroxystyrene) or styrene solution, a polyester film, anethylene-vinyl acetate copolymer film, etc.

Next, another example of recording interference fringes inclined withrespect to the surface of the recording film 2 will be explained withreference to FIGS. 7 to 9. FIG. 7 shows one example of a systemarrangement for carrying out this recording method. In FIG. 7, referencenumeral 1 denotes a series of rolls, 2 a recording film, 3 a transparentmember, and 18 a reflector. The series of rolls 1 feeds the recordingfilm 2 to the space between the transparent member 3 and the reflector18. A feed nozzle 8 supplies the recording film 2 with an index matchingliquid 4 upstream the transparent member 3 and the reflector 18.Reference numeral 5 denotes contact surfaces of the transparent member 3and the reflector 18 with which the recording film 2 is brought intoclose contact through the index matching liquid 4.

FIG. 8 is a sectional view taken along the line A--A' in FIG. 7.Referring to FIGS. 7 and 8, the transparent member 3 has a light beamincidence surface 6 provided on one side thereof at a predeterminedangle to the contact surface 5. Reference numeral 11 denotes a linearincident light beam. The reflector 18 has a reflecting surface 19provided on the bottom thereof. Reference numeral 12 denotes a reflectedlight beam.

Although not shown, surfaces of the transparent member 3 and thereflector 18, exclusive of the light beam incidence surface 6 and thosesurfaces which sandwich the recording film 2, are light-absorbingsurfaces, and portions of the recording film 2 other than a portionthereof where interference is to be caused are shielded from light.

In the above-described arrangement, the light beam 11 is made incidentsubstantially normally on the incidence surface 6. If the angle betweenthe incident light beam 11 and the normal to the incidence surface 6 islarge, reflection occurs at the incidence surface 6, causing the lightbeam utilization efficiency to be lowered. Therefore, the angle of theincident light beam 11 to the normal to the incidence surface 6 ispreferably in the range of from 0° to 10°. The incident light beam 11rectilinearly propagates through the transparent member 3 and reachesthe contact surface 5. The refractive indices of the recording film 2,the transparent member 3, the reflector 18 and the index matching liquid4 are approximately equal to each other. Consequently, the incidentlight beam 11 enters the recording film 2 without reflecting at theinterface between the contact surface 5 and the index matching liquid 4or at the interface between the index matching liquid 4 and therecording film 2 and passes through the index matching liquid 4 at theother side of the film 2 and also through the reflector 18. If the angleΘ ₂ between the incident light beam 11 and the reflecting surface 19 ofthe reflector 18 is small, the incident light beam 11 totally reflectsat the interface between the reflecting surface 19 and the air, so thatthe incident light beam 11 and the reflected light beam 12 interferewith each other in the recording film 2. Thus, interference fringes areformed and recorded in the film 2. If the angle Θ₂ is large, aluminum orthe like may be deposited on the reflecting surface 19 of the reflector18 to form a mirror reflecting layer or a holographic reflecting layer.

In the example shown in FIG. 7 and 8, the contact surface 5 of thetransparent member 3 has a convex cylindrical configuration, and thecontact surface 5 of the reflector 18 has a concave cylindricalconfiguration conformable to the convex cylindrical contact surface 5 ofthe transparent member 3. Accordingly, the recording film 2 can bebrought into close contact with the transparent member 3 and thereflector 18 under favorable conditions with the index matching liquid 4interposed therebetween, so that the recording film 2 can move smoothlywhen fed without being flawed by contact with the contact surfaces 5 andno air bubbles will get mixed in the index matching liquid 4. Thus, thethickness of the index matching liquid 4 can be made small and uniform.In addition, the reverse surface 7 of the recording film 2 will not becontaminated with the index matching liquid 4, and the recording film 2can be uniformly irradiated with the incident light beam 11 and thereflected light beam 12. Accordingly, it is possible to continuouslyrecord a uniform, excellent hologram having a large area. Furthermore,it is only necessary for the transparent member 3 to have a sizerequired for the linear exposure, which is smaller than that in the caseof planar exposure. Thus, the transparent member 3 is small in size andlight in weight and also less costly. In addition, since a linear lightbeam is used, there is substantially no effect of vibration on theexposure. Furthermore, if the reflecting surface 19 that reflects theincident light beam 11 is formed in a convex cylindrical shape along thecontact surfaces 5, the reflected light beam 12 becomes not a parallellight beam but a slightly converging light beam. Accordingly,interference fringes formed by interference between the incident lightbeam 11 and the reflected light beam 12 have a configuration wherein alarge number of interference fringes slightly different in the angle ofinclination are superimposed one on top of another, as shown in FIG.16(c). Accordingly, a holographic mirror obtained in this way alsoprovides a diffraction spectrum which is not a line spectrum but a broadband spectrum due to the disorder of the interference fringes caused bythe cylindrical surface and is therefore suitable for a solar reflectoror the like which reflects light only in the infrared region.

As has been described above, the transparent member 3 and the reflector18 are preferably made of a material having a refractive index close tothat of the recording film 2. Since the refractive index of therecording film 2 is generally in the range of from 1.3 to 1.7, it ispossible to use glass, a plastic material, or an inorganic substance asa material for the transparent member 3 and the reflector 18. It shouldbe noted that since the recording film 2 is exposed to a linear lightbeam applied perpendicularly to the direction of feed of the recordingfilm 2, the exposure is not substantially affected by vibration;however, if the beam irradiation time is long, glass, which hassufficiently large mass and is not readily vibrated, is preferably usedas a material for the transparent member 3 and the reflector 18.

Thus, in this example, the recording film 2 is subjected to linearexposure while being continuously fed in close contact with the contactsurfaces 5 of the transparent member 3 and the reflector 18, whichsandwich the recording film 2 from the upper and lower sides thereof.Accordingly, it is only necessary for the transparent member 3 and thereflector 18 to have a size required for the linear exposure, which issmaller than that in the case of planar exposure. Thus, the transparentmember 3 and the reflector 18 are small in size and light in weight andalso less costly. In addition, since exposure can be effected with therecording film 2 brought into close contact with the transparent member3 and the reflector 18 under favorable conditions, it is possible torealize a hologram of large area and uniform quality. Since a linearlight beam is used, there is substantially no effect of vibration on theexposure.

It should be noted that in FIG. 7 reference numeral 10 denotes anincidence region of the incidence surface 6 on which the linear incidentlight beam 11 is incident. The incident light beam 11 may be formed, forexample, by an arrangement as shown in FIG. 3. That is, a narrow laserbeam 13 is passed through a plano-concave cylindrical lens 14 and aplano-convex cylindrical lens 15, which are disposed in confocalrelation to each other, so that the laser beam 13 is enlarged in onedirection.

As shown in FIG. 8, the incident light beam 11 enters the incidencesurface 6 of the transparent member 3 at substantially right anglesthereto through the incidence region 10 and is reflected at theinterface between the reflecting surface 19 of the reflector 18 and theair or the mirror surface. If reflection occurs elsewhere than thereflecting surface 19 of the reflector 18, the reflected lightundesirably enters the recording film 2 and disorders the interferencefringes. Therefore, surfaces of transparent member 3 and the reflector18, exclusive of the incidence surface 6 and the contact surfaces 5,have previously been subjected to a light-absorbing treatment, therebypreventing irregular reflection. Thus, it is possible to prevent lightfrom undesirably entering an unexposed or exposed portion of therecording film 2 and to thereby prevent the interference fringes frombeing disordered without the need for installing a large-sizedlight-shielding plate.

The difference in refractive index between the recording film 2, thetransparent member 3, the reflector 18 and the index matching liquid 4is preferably not larger than 0.2, more preferably not larger than 0.1,in the temperature range of from 15° C. to 25° C.

If the reflecting surface 19 is disposed not in parallel to the surfaceof the recording film 2 but at a predetermined angle thereto, the angleof reflection of the reflected light beam 12 can be varied. Thus, it ispossible to record inclined interference fringes in the recording film2.

If the reflector 18 is formed in a staircase shape as shown in FIG. 9,it is possible to obtain an advantage in that the material cost of thereflector 18 decreases in addition to an advantageous effect similar tothe above.

The same advantageous effect can also be obtained by forming on thereflecting surface 19 a holographic layer that varies the angle ofreflection instead of varying the angle of the reflecting surface 19.

It should be noted that in the arrangement shown in FIG. 8 the reflector18 is transparent because the reflecting surface 19 is the bottomsurface of the reflector 18. However, the reflecting surface is notnecessarily limited to the bottom surface of the reflector 18, but thecontact surface 5 of the reflector 18 may be used as a reflectingsurface. In such a case, the reflector 18 need not be transparent, andthe reflecting surface, which is the contact surface 5 of the reflector18, may be formed of a mirror reflecting layer or a holographicreflecting layer formed by vapor deposition of aluminum or the like. Ifthe reflecting surface is a mirror reflecting layer formed by vapordeposition of aluminum or the like, it is possible to support therecording film 2 so as to prevent vibration due to the feed of therecording film 2, thereby avoiding an adverse effect on the recording ofinterference fringes. If the reflecting surface is formed of aholographic reflecting layer, it is possible to record obliqueinterference fringes as well as to prevent vibration.

Next, another hologram recording method of the present invention will beexplained. FIG. 10 is a view for explanation of the principle of thisrecording method. A transparent member 22 is brought into close contactwith one surface of the recording film 2, which is successively fed, anda mirror 23 is brought into close contact with the other surface of therecording film 2 in opposing relation to the transparent member 22across the recording film 2. In this state, a light beam 24 is madeincident substantially normally on a surface 22a of the transparentmember 22. The refractive indices of the transparent member 22 and therecording film 2 are approximately equal to each other. Consequently,the light beam 24 enters the recording film 2 without reflecting at theinterface between the transparent member 22 and the recording film 2 andreflects at the interface between the recording film 2 and the mirror23, so that the incident light beam and the reflected light beaminterfere with each other in the recording film 2. Thus, a hologram isrecorded in the recording film 2. If the recording film 2 iscontinuously fed, a hologram of large area can be recorded.

FIG. 11 is a view for explanation of a continuous exposure, roll-feedsystem. In the arrangement shown in FIG. 11, the recording film 2 iswound close on a mirror-finished roll 25, and the transparent member 22is brought into close contact with the upper side of the recording film2. In this state, the light beam 24 is made incident substantiallynormally on the surface 22a of the transparent member 22 and reflectedat the surface of the mirror-finished roll 25, thereby causing theincident light beam and the reflected light beam to interfere with eachother in the recording film 2. Thus, interference fringes are formed andrecorded in the recording film 2. By continuously feeding the recordingfilm 2, holograms can be continuously recorded.

As has been described above, the transparent member 22 is preferablymade of a material having a refractive index close to that of therecording film 2. Since the refractive index of the recording film 2 isgenerally in the range of from 1.3 to 1.7, it is possible to use glass,a plastic material, or an inorganic substance as a material for thetransparent member 3. Further, since a linear light beam is employed,the exposure is not substantially affected by vibration; however, if thebeam irradiation time is long, it is preferable to use glass as amaterial for the transparent member 3.

Thus, in this example, the recording film 2 is subjected to linearexposure with the transparent member 22 brought into close contact withit and with the roll 25 rotated. Accordingly, the amount of transparentmaterial required for the transparent member 22 is minimized. Thus, thetransparent member 22 becomes less costly, thin, small in size and lightin weight. In addition, since continuous exposure can be effected, ahologram of large area can be realized. Since linear exposure isemployed, the effect of vibration is minimized. Further, since thesurface of the roll 25 is mirror-finished, the transparent member 22needs to be disposed only at one side of the recording film 2.

As shown in FIG. 12(a), the light beam 24 enters the surface 22a of thetransparent member 22 at substantially right angles thereto and isreflected by the mirror surface of the roll 25 at the reverse side ofthe recording film 2. If reflection occurs at a surface 22b of thetransparent member 22, the reflected light undesirably enters therecording film 2 and disorders the interference fringes. Therefore, thesurface 22b has previously been subjected to a light-absorbing treatmentto prevent irregular reflection, as shown in FIG. 12(b). Thus, disorderof the interference fringes can be prevented.

It is also possible to dispose a transparent member 26 at the lower sideof the roll 25, as shown in FIG. 13. In the arrangement shown in FIG.13, the surface of the transparent member 26 that faces the roll 25 isan arcuate surface conformable to the surface of the roll 25, and theindex matching liquid 4 is dropped onto the arcuate surface. In thisstate, the recording film 2 is wound on the roll 25 and brought intoclose contact with the roll 25 and the transparent member 26 by gravity.Thus, the recording film 2 can be brought into close contact with theroll 25 and the transparent member 26 under favorable conditions, andunnecessary stray light can be eliminated. Accordingly, a hologram ofgood quality can be produced. In this case also, it is preferable thatsurfaces of the transparent member 26 on which no light beam will beincident have previously been subjected to a light-absorbing treatment.

Next, the hologram recording method of the present invention, which usesthe system arrangements shown in FIGS. 1 to 13, will be explained morespecifically by way of examples.

(Example 1)

As shown in FIGS. 1 and 2, a recording film 2 (Omnidex 352, a roll film1 foot in width and 500 feet in length, manufactured by Du Pont Co.,Ltd.) was brought into close contact through an index matching liquid 4(xylene) with a glass block 3 having a convexly curved surface 5 as asurface coming in contact with the recording film 2 and a lightincidence surface 6, the other surfaces of the glass block 3 having beensubjected to an antireflection treatment by painting them black.

Next, as shown in FIG. 3, light 13 of wavelength 514 nm oscillated froman Ar laser was incident on the concave surface of a plano-concavecylindrical lens 14 and then on the convex surface of a plano-convexcylindrical lens 15 to form a slit-shaped parallel light beam 11. Thelight beam 11 was then made incident on the surface 6 of the glass block3 at an angle Θ of 30° and at a light intensity of 60 mW/cm² to 75mW/cm².

In this state, the recording film 2 was continuously fed at a speed of0.5 cm/sec. As a result, interference fringes with a pitch of 370 nmwere recorded in the recording film 2 over an area 1 foot in width and450 feet in length in a direction substantially parallel to therecording layer of the recording film 2.

Thereafter, the recording film 2 was irradiated with ultraviolet raysfor 1 minute and baked for 1 hour at 100° C., thereby obtaining adiffraction grating having a diffraction efficiency of 46% at awavelength of 1,110 nm.

The diffraction efficiency was measured as follows. After the formationof the interference fringes, the recording film 2 was cut into a pieceabout 5 by 5 cm square. The test sample was set in a spectrophotometer(Shimazu double monochromator autographic spectrophotometer UV-365,manufactured by Shimazu Seisakusho Ltd.), and the transmittance withrespect to normally incident light in the wavelength range of from 1,400nm to 400 nm was measured. The value obtained by subtracting themeasured transmittance from 100% was regarded as the reflectivity, thatis, the diffraction efficiency.

After the formation of the interference fringes, the film was cut into alength of 100 cm, and the cut piece of film was pasted on a windowglass. The film reflected solar infrared rays in the region of 1,110 nm,resulting in a lowering of the temperature in the vicinity of the windowglass.

(Example 2)

A composition having the following chemical composition was dissolved in10 g of 1,4-dioxane, and the resulting solution was filtered through afilter having a pore diameter of 0.25 μm to obtain a photosensitivesolution. ##STR1##

The photosensitive solution was coated on a PET film (HP-7, manufacturedby Teijin Limited), which had a thickness of 100 μm and had previouslybeen subjected to internal primer coating, by using a roller coater sothat the dry film thickness was 5 μm, and then dried for 45 minutes at70° C. Thereafter, an aqueous solution of 10% polyvinyl alcohol (PVA205,manufactured by Kuraray Co., Ltd.; degree of polymerization 500; anddegree of saponification 88%) was coated thereon by using a rollercoater. The film coated with the solution was dried for 10 minutes at60° C., thereby obtaining a recording film 2.

Then, the recording film 2 was continuously fed at a speed of 0.9 cm/secin a state as shown in FIG. 4, with the polyvinyl alcohol coatingsurface facing downward and the PET film base material surface facingupward. As the index matching liquid 4, bromobenzene (refractive index1.56) was used in order to make the refractive index close to that ofthe recording film 2. In this state, light of wavelength 488 nmoscillated from an Ar laser was made incident on a block of a polyesterresin material (refractive index 1.57) at an angle Θ of 27.7° and at alight intensity of 28 mW/cm² thereby recording interference fringes inthe recording film 2.

After the exposure by the Ar laser, the recording film 2 was exposed atan exposure of 0.1 J/cm² by using an ultraviolet radiation lamp(Chemical Lamp FL-20BL, trade name, manufactured by Toshiba Corp.). Atthis time, a sharp cut filter L39 was employed so that only visiblelight of wavelength 400 nm or longer was applied to the recording film2.

After the exposure, the recording film 2 was washed in a running waterbath for 1 minute, thereby removing the polyvinyl alcohol layer.Thereafter, the recording film 2 was dried.

Next, the recording film 2 was dipped for 2 minutes in an acetone bathand then dipped for 1 minute in a heptane bath.

The diffraction efficiency of the hologram thus obtained was measured inthe same way as in Example 1. It was 78% at a wavelength in the regionof 950 nm. That is, it was possible to obtain a diffraction gratinghaving a diffraction efficiency of 78% and comprising interferencefringes with a pitch of 302 nm which were recorded in a directionapproximately parallel to the recording layer of the recording film 2.The value of diffraction efficiency, i.e., 78%, was uniform throughoutthe recording film 2 within ±3%.

It should be noted that the above-described refractive index values weremeasured at D-lines of sodium with an Abbe's refractometer.

(Example 3)

In the arrangement shown in FIG. 6, the protective film 16 was formed bydie-coating the following recording film 2 with an aqueous solution of apolyvinyl alcohol (degree of saponification 88%; and degree ofpolymerization 500) so that the angle Θ₃ of the reflecting surface 17was 5°. The transparent member 3 had a cylindrical recording filmcontact surface 5 and a light incidence surface 6, as shown in FIGS. 1and 6, and surfaces of the transparent member 3, exclusive of thecontact surface 5 and the incidence surface 6, had previously beensubjected to an antireflection treatment by painting them black.

The recording film 2 (Omnidex 352, a film 1 foot in width and 500 feetin length, manufactured by Du Pont Co., Ltd.) was brought into closecontact with the transparent member 3 through xylene used as an indexmatching liquid 4.

Next, as shown in FIG. 3, light 13 of wavelength 514 nm oscillated froman Ar laser was incident on the concave surface of a plano-concavecylindrical lens 14 and then on the convex surface of a plano-convexcylindrical lens 15 to form a slit-shaped parallel light beam 11. Thelight beam 11 was then made incident on the surface 6 of the glass block3 at an angle Θ₁ of 20° and at a light intensity of 60 mW/cm² to 75mW/cm².

In this state, the recording film 2 was continuously fed at a speed of 1cm/sec. As a result, interference fringes having a pitch of about 400 nmand inclined at 5° with respect to the film surface were recorded in therecording film 2 over an area 1 foot in width and 450 feet in length.

Thereafter, the recording film 2 was irradiated with ultraviolet raysfor 1 minute by using an H-bulb lamp for F-450, manufactured by FusionCo. Ltd., and baked for 1 hour at 100° C. thereby obtaining adiffraction grating having a diffraction efficiency of 50% at awavelength of 1,200 nm. The diffraction efficiency was measured in thesame way as in Example 1.

When the film was inclined at 5° the above maximum diffractionefficiency was obtained.

After the formation of the interference fringes, the film was cut into apiece of a window glass size, and the cut piece of film was pasted on awindow glass so that the sunlight was incident nearly normally on theinclined interference fringes. The film reflected solar infrared rays inthe region of 1,200 nm, resulting in a lowering of the temperature inthe vicinity of the inside of the window glass. When the film was peeledfrom the window glass, a rise in temperature was observed.

(Example 4)

A photosensitive solution having the same chemical composition as thatin Example 2 was coated on a PET film (HP-7, manufactured by TeijinLimited), which had a thickness of 100 μm and had previously beensubjected to internal primer coating, by using a roller coater so thatthe dry film thickness was 8 μm, and then dried for 45 minutes at 70° C.Thereafter, a solution of 30% poly(p-hydroxystyrene) in isopropylalcohol was coated thereon by using a dip coater. The film coated withthe solution was transported being erected in a direction perpendicularto the direction of the film thickness, and after 5 seconds had elapsed,the film was dried for 10 minutes at 60° C., thereby obtaining arecording film 2.

Then, the recording film 2 was continuously fed at a speed of 0.9cm/sec, and in this state, light of wavelength 488 nm oscillated from anAr laser was made incident on a transparent member 3 made of F2 glass(manufactured by (K.K.) Miyuki Kogaku Kogyo; refractive index 1.61989)at an angle Θ₁ of 13° and at a light intensity of 28 mW/cm², therebyrecording interference fringes in the recording film 2.

After the exposure by the Ar laser, the recording film 2 was exposed atan exposure of 0.1 J/cm² by using an ultraviolet radiation lamp(Chemical Lamp FL-20BL, manufactured by Toshiba Corp.). At this time, asharp cut filter L39 was employed so that only visible light ofwavelength 400 nm or longer was applied to the recording film 2.

After the exposure, the recording film 2 was washed in an isopropylalcohol bath for 1 minute, thereby removing the poly(p-hydroxystyrene)layer. Thereafter, the recording film 2 was dried.

Next, the recording film 2 was dipped for 2 minutes in an acetone bathand then dipped for 1 minute in a heptane bath.

The diffraction efficiency of the hologram thus obtained was measured inthe same way as in Example 1. It was 78% at a wavelength in the regionof 950 nm due to contraction after the development. That is, it waspossible to obtain a diffraction grating having a diffraction efficiencyof 78% and comprising interference fringes with a pitch of about 298 nmwhich were recorded at an inclination angle of 8° with respect to therecording layer of the recording film 2. The value of diffractionefficiency, i.e., 78%, was uniform throughout the recording film 2within ±3%.

It should be noted that the above-described refractive index values weremeasured at D-lines of sodium with an Abbe's refractometer.

(Example 5)

A reflector 18 made of a glass block material was used. The angle Θ₃(see FIG. 8) of the reflecting surface 19 of the reflector 18 was set at20°. As shown in FIGS. 7 and 8, the recording film contact surface 5 ofthe transparent member 3 had a convex cylindrical configuration, whereasthe contact surface 5 of the reflector 18 had a concave cylindricalconfiguration conformable to the convex contact surface 5 of thetransparent member 3. Surfaces of the transparent member 3 and thereflector 18, exclusive of the light incidence surface 6 and thecylindrical contact surfaces 5, had previously been subjected to anantireflection treatment by painting them black.

A recording film 2 (Omnidex 352, a film 1 foot in width and 500 feet inlength, manufactured by Du Pont Co., Ltd.) was brought into closecontact with the transparent member 3 and the reflector 18 throughxylene used as an index matching liquid 4.

Next, as shown in FIG. 3, light 13 of wavelength 514 nm oscillated froman Ar laser was incident on the concave surface of a plano-concavecylindrical lens 14 and then on the convex surface of a plano-convexcylindrical lens 15 to form a slit-shaped parallel light beam 11. Thelight beam 11 was then made incident on the surface 6 of the glass block3 at an angle Θ₁ of 10° and at a light intensity of 60 mW/cm² to 75mW/cm².

In this state, the recording film 2 was continuously fed at a speed of 1cm/sec. As a result, interference fringes having a pitch of about 370 nmand inclined at 20° with respect to the film surface were recorded inthe recording film 2 over an area 1 foot in width and 450 feet in lengthin a direction substantially parallel to the recording layer of therecording film 2.

Thereafter, the recording film 2 was irradiated with ultraviolet raysfor 1 minute by using an H-bulb lamp for F-450, manufactured by FusionCo. Ltd., and baked for 1 hour at 100° C., thereby obtaining adiffraction grating having a diffraction efficiency of 50% at awavelength of 1,100 nm. The diffraction efficiency was measured in thesame way as in Example 1.

When the film was inclined at 20°, the above maximum diffractionefficiency was obtained.

After the formation of the interference fringes, the film was cut into apiece of a window glass size, and the cut piece of film was pasted on awindow glass so that the sunlight was incident nearly normally on theinclined interference fringes. The film reflected solar infrared rays inthe region of 1,110 nm, resulting in a lowering of the temperature inthe vicinity of the inside of the window glass. When the film was peeledfrom the window glass, a rise in temperature was observed.

(Example 6)

A photosensitive solution having the same chemical composition as thatin Example 2 was coated on a PET film (HP-7, manufactured by TeijinLimited), which had a thickness of 100 μm and had previously beensubjected to internal primer coating, by using a roller coater so thatthe dry film thickness was 5 μm, and then dried for 45 minutes at 70° C.Thereafter, an aqueous solution of 10% polyvinyl alcohol (manufacturedby Kuraray Co., Ltd.; degree of polymerization 500; and degree ofsaponification 88%) was coated thereon by using a roller coater. Thefilm coated with the solution was dried for 10 minutes at 60° C. therebyobtaining a recording film 2.

Next, with a staircase-shaped reflector 18 (Θ₃ =15°) as shown in FIG. 9used, the recording film 2 was continuously fed at a speed of 0.9cm/sec. As the index matching liquid 4, xylene was used in order to makethe refractive index close to that of the recording film 2. In thisstate, light of wavelength 488 nm oscillated from an Ar laser was madeincident on a transparent member 3 of F2 glass (manufactured by (K.K.)Miyuki Kogaku Kogyo; refractive index 1.61989) at an angle Θ₁ of 13° andat a light intensity of 28 mW/cm², thereby recording interferencefringes in the recording film 2.

After the exposure by the Ar laser, the recording film 2 was exposed atan exposure of 0.1 J/cm² by using an ultraviolet radiation lamp(Chemical Lamp FL-20BL, manufactured by Toshiba Corp.). At this time, asharp cut filter L39 was employed so that only visible light ofwavelength 400 nm or longer was applied to the recording film 2.

After the exposure, the recording film 2 was washed in a running waterbath for 1 minute, thereby removing the polyvinyl alcohol layer.Thereafter, the recording film 2 was dried.

Next, the recording film 2 was dipped for 2 minutes in an acetone bathand then dipped for 1 minute in a heptane bath.

The diffraction efficiency of the hologram thus obtained was measured inthe same way as in Example 1. It was 78% at a wavelength in the regionof 1,000 nm. That is, it was possible to obtain a diffraction gratinghaving a diffraction efficiency of 78% and comprising interferencefringes with a pitch of about 310 nm which were recorded at aninclination angle of 15° with respect to the recording layer of therecording film 2. The value of diffraction efficiency was uniformthroughout the recording film 2 within ±3%.

It should be noted that the above-described refractive index values weremeasured at D-lines of sodium with an Abbe's refractometer.

(Example 7)

As shown in FIG. 14, a roll 25, a film supply roll 31, and a take-uproll 32 were supported by respective support rods 33, 34 and 35 andrespective shockabsorbing desks 36, 37 and 38. Air was injected into theshockabsorbing desks 36, 37 and 38 to provide shockabsorbing effect. Theroll 25 had a light-reflecting surface formed by chrome plating. As therecording film 2, Omnidex 352 (manufactured by Du Pont Co. Ltd.) havinga width of 30 cm was used. The recording film 2 was brought into closecontact with the roll 25 through xylene used as an index matchingliquid. A glass block 30 was brought into close contact with therecording film 2 through xylene used as an index matching liquid. As anincident light beam, light of wavelength 488 nm emitted from an Ar laserwas diffused through a spatial filter and then formed into a parallelbeam of light by a parabolic mirror. The light beam was made incident ona surface 30a of the glass block 30 at an angle Θ of 15°. In this state,the recording film 2 was exposed at an exposure of 20 mJ/cm². As aresult, interference fringes with a pitch of 1.4 μm were recorded in therecording film 2 in parallel to the film surface. Thereafter, therecording film 2 was baked for 2 hours at 120° C., thereby obtaining adiffraction grating having a diffraction efficiency of 70%. However,unnecessary rainbow due to reflection at the interfaces 30b and 30cbetween the glass block 30 and the air was observed.

(Example 8)

The surfaces 30b and 30c of the glass block 30 in Example 7 weresubjected to an antireflection treatment, and recording was carried outusing this glass block 30 in the same way as in Example 7. As a result,a diffraction efficiency similar to the above was obtained, andunnecessary rainbow was not observed any longer.

After the interference fringes had been formed in this way, therecording film 2 was cut into a piece 55 by 55 cm square, and the cutpiece of film was pasted on a window glass. The film reflected solarinfrared rays in the region of 1.4 μm, resulting in a lowering of thetemperature in the room.

(Example 9)

The roll 25 and the transparent member 26 were arranged as shown in FIG.13. Omnidex 352 (manufactured by Du Pont Co. Ltd.; a roll film having awidth of 30 cm) used as a recording material was brought into closecontact with the chrome-plated roll 25 through xylene used as an indexmatching liquid. Surfaces of the transparent member 26 on which no lightwould be incident had previously been subjected to an antireflectiontreatment. The index matching liquid of xylene was dropped onto thesurface of the transparent member 26 that faced the roll 25, and theroll 25 having the recording film brought into contact therewith wasplaced thereon, thereby bringing the recording film 2 into close contactwith the roll 25 and the transparent member 26 by gravity. The recordingfilm 2 was allowed to stand for 2 minutes in this state. Then, recordingwas carried out in the same way as in Example 7. As a result,interference fringes similar to those in Example 8 were obtained.

The hologram recording method described in the foregoing examples is oneexample of the present invention, and the present invention is notlimited to these examples.

It will be apparent that in the method of the present invention whereininterference fringes are obliquely recorded, the recording film may beeither fed or unmoved. Further, it will be apparent that the feed of therecording film may be either continuous or intermittent. Further, itwill also be apparent that the exposure process may be either continuousor intermittent.

It is a matter of course that the present invention can be carried outin various forms within the scope of the invention and that these formsare included in the present invention.

As will be clear from the foregoing description, according to thehologram recording method and recorded hologram of the presentinvention, a transparent member is disposed at one surface of arecording film, and the space between the recording film and the filmcontact surface of the transparent member is filled with an indexmatching liquid so that the recording film is brought into close contactwith the transparent member through the index matching liquid. In thisstate, a light beam is made incident on a surface of the transparentmember other than the recording film contact surface so that theincident light beam reaching the recording film through the contactsurface and the light beam reflected from the interfacial boundarybetween the reverse surface of the recording film and the air interferewith each other in the recording film, thereby forming and recordinginterference fringes in the recording film. Accordingly, even if theangle of incidence of the light beam to the surface of the recordingfilm is small, exposure of high efficiency can be realized. In addition,it is possible to select various pitches for interference fringes to berecorded by varying the angle of the incident light beam to the surfaceof the recording film.

If a recording film of continuous length is subjected to exposure usinga linear light beam while being continuously fed, it becomes possible toreadily produce a uniform, high-quality hologram having a large area.Thus, it is possible to provide a hologram producing method which givesa high yield and is suitable for mass-production.

Further, a surface of the transparent member that is brought into closecontact with the recording film is convexly curved only in the directionof feed of the recording film, and the space between the recording filmcontact surface and the recording film is filled with an index matchingliquid so that the recording film is brought into close contact with thetransparent member through the index matching liquid. Therefore, thecondition of contact between the recording film and the transparentmember improves, so that the recording film moves smoothly when fed.Accordingly, the recording film will not be flawed by contact with thecontact surface of the transparent member, and no air bubbles will getmixed in the index matching liquid. Thus, the thickness of the indexmatching liquid can be made small and uniform. In addition, the reversesurface of the recording film will not be contaminated with the indexmatching liquid, and the recording film can be uniformly irradiated withthe incident light beam and the reflected light beam. Accordingly, it ispossible to continuously record a uniform, excellent hologram having alarge area. Furthermore, interference fringes can be formed in therecording film such that a large number of interference fringes slightlydifferent in the angle of inclination are superimposed one on top ofanother by virtue of the configuration of the contact surface of thetransparent member. Therefore, a holographic mirror thus recorded in therecording film provides a diffraction spectrum which is not a linespectrum but a broad band spectrum. Accordingly, it is possible toobtain a holographic mirror suitable for a solar reflector or the likewhich reflects light only in the infrared region.

If a surface of the recording film that will not come in contact withthe transparent member is formed with a layer having a thicknessdistribution in a direction perpendicular to the direction of feed ofthe recording film so that the incident light beam is reflected at thislayer, it is possible to form interference fringes inclined with respectto the surface of the recording film. Thus, the method is suitable forproduction of a solar reflector or the like.

If surfaces of the transparent member, exclusive of the light beamincidence surface and the recording film contact surface, havepreviously been subjected to a light-absorbing treatment, it is possibleto prevent irregular reflection and to minimize the disorder ofinterference fringes. In addition, no light will impinge on portions ofthe recording film other than the exposed portion thereof. Thus, itbecomes unnecessary to install a large-sized light-shielding plate.

What we claim is:
 1. A method of recording a hologram in a continuouslyfed recording film by interference of light, said methodcomprising:disposing a transparent member, which is elongated in adirection traverse to a direction of feed of said recording film, at onesurface of said recording film, said transparent member having a surfacewhich is brought into close contact with said recording film, saidcontact surface being convexly curved only in said direction of feed ofsaid recording film; bringing said recording film into close contactwith said transparent member through an index matching liquid filling aspace between said contact surface and said recording film; and making abeam of light incident on a surface of said transparent member otherthan said contact surface so that the incident light beam reaching saidrecording film through said contact surface and the light beam reflectedfrom an interfacial boundary between a reverse surface of said recordingfilm and air interfere with each other in said recording film, therebyforming and recording interference fringes in said recording film.
 2. Ahologram recording method according to claim 1, wherein said light beam,which is made incident on a surface of said transparent member otherthan said contact surface, is a light beam that is reciprocated to scanin a direction intersecting the direction of feed of said recording filmso that the scanning light beam reaching said recording film throughsaid contact surface and the light beam reflected from the interfacialboundary between the reverse surface of said recording film and the airinterfere with each other in said recording film, thereby forming andrecording interference fringes in said recording film.
 3. A hologramrecording method according to claim 2, wherein said interference fringeshave broad wavelength.
 4. A hologram recording method according to claim1, wherein a surface of said recording film on a side thereof which willnot come in contact with said transparent member is formed with a layerhaving a thickness distribution in a direction perpendicular to thedirection of feed of said recording film so that the incident light beamis reflected at the surface of this layer.
 5. A hologram recordingmethod according to any one of claims 1, 2 or 4, wherein surfaces ofsaid transparent member, exclusive of said light beam incidence surfaceand said contact surface, have previously been subjected to alight-absorbing treatment, and portions of said recording film otherthan the irradiated portion thereof are shielded from light.
 6. Ahologram recording method according to claim 4, wherein said layerhaving a thickness distribution has a distribution in which the layerthickness gradually increases.
 7. A hologram recording method accordingto claim 6, wherein an angle between the surface of said layer havingthe thickness distribution and the surface of said recording film islarger than 0° and not larger than 10°.
 8. A hologram recording methodaccording to claim 4, wherein the interference fringes recorded in saidrecording film are inclined at an angle larger than 0° and not largerthan 10° with respect to the film surface.
 9. A hologram recordingmethod according to claim 1, wherein said interference fringes havebroad wavelength.
 10. A hologram recording method according to any oneof claims 1, 2 or 4, wherein said transparent member is made of amaterial having a refractive index differing from that of said recordingfilm by 0.2 or less in the temperature range of from 15° C. to 25° C.11. A hologram recording method according to claim 10, wherein aprincipal component of said recording film is a polyvinyl carbazolederivative, and said transparent member is made of F2 glass, a polyesterresin, an allyl resin having a high refractive index, or an acrylicresin having a high refractive index.
 12. A hologram recording methodaccording to claim 10, wherein a principal component of said recordingfilm is a polyvinyl acetate derivative, and said transparent member ismade of BK-7 glass or quartz glass.
 13. A hologram recording methodaccording to claim 10, wherein a principal component of said recordingfilm is a polyester, and said transparent member is made of F2 glass.14. A hologram recording method according to any one of claims 1 to 3,wherein said light beam is incident on said incidence surface of saidtransparent member at an angle of 90°±10° to said incidence surface. 15.A hologram recording method according to claim 14, wherein said lightbeam is not substantially reflected or refracted as said light beamtravels from said incident surface to said recording film.
 16. Ahologram recording method according to any one of claims 1, 2 or 4,wherein said contact surface has a curvature radium in the range of from10 mm to 100 mm.
 17. A hologram recording method according to any one ofclaims 1, 2 or 4, wherein an angle made between one side surface of saidtransparent member and said recording film when said recording filmcomes in contact with said contact surface and an angle made betweenanother side surface of said transparent member and said recording filmwhen said recording film comes out of the contact with said contactsurface are both in the range of from 5° to 45°.
 18. A hologramrecording method according to any one of claims 1, 2 or 4, wherein asize of said incident light beam in the direction of feed of saidrecording film is not larger than 3 mm with regard to beam sizes whichprovide at least 13.5% of a maximum intensity.
 19. A hologram recordingmethod according to any one of claims 1, 2 or 4, wherein a tension of 10kg/m to 50 kg/m is applied to said recording film, and the thickness ofsaid index matching liquid between said recording film and said contactsurface is not larger than 500 μm.
 20. A hologram recording methodaccording to any one of claims 1, 2 to 4, Wherein said transparentmember is disposed at an upper side of said recording film.
 21. Ahologram recording method according to any one of claims 1, 2 or 4,wherein said transparent member is disposed at a lower side of saidrecording film.
 22. A method of recording a hologram in a continuouslyfed recording film by interference of light, said methodcomprising:sandwiching said recording film between a transparent member,which is elongated in a direction traverse to a direction of feed ofsaid recording film, disposed at a side where a light beam enters and areflector disposed at a side where the light beam reflects, wherein saidtransparent member has a contact surface which contacts said recordingfilm and a light incidence surface which is different than said contactsurface and wherein said contact surface is convexly curved only in saiddirection of feed of said recording film; and making the light beamincident on said light incidence surface so that the incident light beamreaching said recording film and the light beam transmitted by saidrecording film and reflected from a reflecting surface of said reflectorinterfere with each other in said recording film, thereby forming andrecording interference fringes in said recording film.
 23. A hologramrecording method according to claim 22, wherein said interferencefringes have broad wavelength.
 24. A hologram recording method accordingto claim 22, wherein said reflecting surface and the surface of saidrecording film are disposed at an angle to each other to vary the angleof the reflected light beam to thereby record oblique interferencefringes in said recording film.
 25. A hologram recording methodaccording to claim 22, or 24, wherein said reflecting surface is formedin a staircase shape to make an angle between said reflecting surfaceand the surface of said recording film, thereby varying the angle ofsaid reflected light beam, and thus recording oblique interferencefringes in said recording film.
 26. A hologram recording methodaccording to claim 22, or 24, wherein said reflecting surface has aholographic reflecting layer thereon so that the angle of said reflectedlight beam is varied by said holographic reflecting layer, therebyrecording oblique interference fringes in said recording film.
 27. Ahologram recording method according to claim 22 or 24, wherein a linearlight beam is used as said incident light beam, and said recording filmis fed along the respective recording film contact surfaces of saidtransparent member and said reflector.
 28. A hologram recording methodaccording to claim 22 or 24, wherein one of said recording film contactsurfaces of said transparent member and said reflector is a convexsurface, and the other is a concave surface.
 29. A hologram recordingmethod according to claim 22 or 24, wherein a space between saidrecording film and said transparent member is filled with an indexmatching liquid so that said recording film is brought into closecontact with said transparent member through said index matching liquid.30. A hologram recording method according to claim 29, wherein a spacebetween said recording film and said reflector is filled with an indexmatching liquid so that said recording film is brought into closecontact with said reflector through said index matching liquid.
 31. Ahologram recording method according to claim 22 or 24, wherein adifference between refractive indices of said transparent member, saidrecording film and said index matching liquid is not larger than 0.2 inthe temperature range of from 15° C. to 25° C.
 32. A hologram recordingmethod according to claim 22 or 24, wherein said reflector is atransparent member, and a difference between refractive indices of saidreflector, said recording film and said index matching liquid is notlarger than 0.2 in the temperature range of from 15° C. to 25° C.
 33. Ahologram recording method according to claim 22 or 24, wherein saidreflecting surface of said reflector is said recording film contactsurface.
 34. A hologram recording method according to claim 22 or 24,wherein said reflector has said reflecting surface elsewhere than saidrecording film contact surface.
 35. A hologram recording methodaccording to claim 22 or 24, wherein said reflecting surface defines aninterface in cooperation with air.
 36. A hologram recording methodaccording to claim 22 or 24, wherein said reflecting surface has amirror reflecting layer thereon.
 37. A hologram recording methodaccording to claim 22 or 24, wherein surfaces of said transparentmember, exclusive of said light incidence surface and said recordingfilm contact surface, are light-absorbing surfaces, and portions of saidrecording film other than the portion thereof where said interference isto be caused are shielded from light.
 38. A hologram recording methodaccording to claim 22 or 24, wherein an angle between a normal to saidlight incidence surface and said incident light beam is in the range offrom 0° to 10°.
 39. A hologram recording method according to claim 38,wherein said light beam is not substantially reflected or refracted assaid light beam travels from said light incident surface toward saidrecording film.
 40. A hologram recording method according to claim 22 or24, wherein a space between said recording film and said reflector isfilled with an index matching liquid so that said recording film isbrought into close contact with said reflector through said indexmatching liquid.
 41. A hologram comprising equally spaced interferencefringes recorded in a recording film, wherein said interference fringesare parallel to at least one direction of a plane of said recordingfilm, wherein disorder of the interference fringes in a cross-sectionalong said direction is larger than disorder of the interference fringesin a cross-section along a direction perpendicular to said direction.42. A hologram according to claim 41, wherein the interference fringesin the cross-section along the direction perpendicular to thefirst-mentioned direction are at an angle to the plane of said recordingfilm.